An essential aspect of plant metabolism is the use of nitrates and other inorganic nitrogen compounds in the synthesis of organic compounds such as amino acids, proteins, chlorophylls, vitamins, hormones and alkaloids which are essential to plant growth and development. Although plants absorb nitrates and other nitrogen compounds from the soil, the ultimate source of nitrogen is the free dinitrogen (N.sub.2) of the atmosphere; however, free dinitrogen as such, must be fixed and converted to a form that can be utilized by the plant.